This invention relates in general to projection type television systems having shutdown circuits for protection in the event of failures and particularly to on/off circuits useful with such shutdown circuits.
Interest in large screen television systems using optical projection for achieving large video displays is increasing. Most such systems incorporate three small single-color cathode ray tubes (CRT's) with corresponding projection lenses for simultaneously and convergently displaying the three independent color pictures upon either a large projection screen or upon a blank light-colored area, such as a wall. To achieve suitable brightness levels the individual color CRT's are driven at very high levels which creates a substantial amount of heat. A form of protection, known as a shutdown circuit is provided for disabling the CRT circuitry in the event of a malfunction in the system which could impose destructive operating conditions on the CRT's.
With the increasing use of video tape recorders, video games, and portable computers, which do not have associated display systems, a demand for video monitors has arisen. While the demand is greatest for monochrome monitors, there is a growing need for color monitors and for large display color projection monitors.
A monitor by definition, is a "stand alone" device and therefore needs its own power switch. With the growing use of microprocessor-based electronic equipment, on/off switches of the low voltage, momentary contact type have found increasing favor. Such switches provide line isolation, ease of operation and user compatability with present day equipment. They are also very simple and reliable.